Method of forming a metal to polysilicon contact in oxygen environment

ABSTRACT

A method for forming a contact capable of tolerating an O 2  environment up to several hundred degrees Celsius for several hours is disclosed. To slow down the metal oxide front of the metal layer at the metal-polysilicon interface, the metal layer is surrounded by one or more oxygen sink spacers and layers. These oxygen sink spacers and layers are oxidized before the metal layer at the bottom of the plug is oxidized. Accordingly, the conductive connection between the polysilicon and any device built on top of the barrier layer is preserved.

This application is a continuation application of U.S. patentapplication Ser. No. 09/930,268, filed Aug. 16, 2001, now U.S. Pat. No.6,472,326 which in turn is a divisional application of U.S. patentapplication Ser. No. 09/650,071, filed Aug. 29, 2000 now U.S. Pat. No.6,583,460 the entirety of both being incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to the field of semiconductor integratedcircuits and, in particular, to metal-polysilicon contacts capable oftolerating high temperature oxidizing environments.

BACKGROUND OF THE INVENTION

Semiconductor integrated circuits with high device density poseincreasing difficulty to the formation of high-reliability electricalconnections between metalization layers and semiconductor elements,particularly between the metal of a metallic electrode and the adjacentpolysilicon of a polysilicon plug. This increased difficulty stemsmainly from the tendency of metal and silicon to interdiffuse when incontact with each other, and when subjected to the high temperaturesnecessary during the fabrication of integrated circuits.

To illustrate the tendency of metal-silicon interdiffusion, theformation of a metallic contact between a polysilicon plug and ametallic electrode at a specified contact area will be briefly describedbellow. FIG. 1 depicts a portion of a conventional memory cellconstruction for a DRAM at an intermediate stage of the fabrication, inwhich a metal-polysilicon contact is formed according to conventionalprocesses.

A pair of memory cells having respective access transistors 33 areformed within a well 13 of a substrate 12. The wells and transistors aresurrounded by a field oxide region 14 that provides isolation. N-typeactive regions 16 are provided in the doped p-type well 13 of substrate12 (for NMOS transistors) and the pair of access transistors haverespective gate stacks 30. The gate stacks 30 include an oxide layer 18,a conductive layer 20, such as poly silicon, nitride spacers 32, and anitride cap 22. Additional stacks 31 may also be formed for use inperforming self aligned contact etches to form conductive plugs forcapacitor structures in the region between stacks 30,31. The details ofthese steps are well-known in the art and are not described in thisapplication.

Next, a polysilicon plug 50 (FIG. 1) is formed in a contact opening of afirst insulating layer 24, to directly connect to a source or drainregion 16 of the semiconductor device. The first insulating layer 24could be, for example, borophosphosilicate glass (BPSG), borosilicateglass (BSG), or phosphosilicate glass (PSG). Once the polysilicon plug50 is formed, the whole structure, including the substrate 12 with thegate stacks 30, tie first insulating layer 24 and the polysilicon plug50, is chemically or mechanically polished to provide a planarizedsurface.

At this point, a second insulating layer 25, which can be of the samematerial as that of the first insulating layer 24, is deposited over thefirst insulating layer 24 and the polysilicon plug 50. A contact openingor via is etched over the polysilicon plug 50 and a metal layer or metalelectrode 55 is then deposited and patterned to connect to thepolysilicon plug 50, as illustrated in FIG. 1. Thus, polysilicon plug 50comes into contact with the metal layer or electrode 55 at ametal-polysilicon interface 51 (FIG. 1). It must be understood, however,that, as known in the art, any other conductor, such as a capacitorplate for example, may also be in contact with a polysilicon plug, andthe discussion herein applies to any metal-polysilicon interface.

Since several steps during the IC fabrication require temperatureshigher than 500° C., such as annealing steps, for example, silicon fromthe polysilicon plug 50 migrates into the metal film of the metallicelectrode 55 during these high-temperature steps. Although this siliconmigration into the metal film occurs in limited regions, near or at themetal-polysilicon interface 51, since the migrated silicon has highresistivity, the contact resistance at the metal-polysilicon interface51 is greatly increased.

Barrier layers have been introduced to solve the silicon diffusionproblem at the metal-polysilicon contact, such as interface 51 (FIG. 1).A barrier layer 52 is illustrated in FIG. 2 (which shows only a middleportion of the structure of FIG. 1). Conventionally, the barrier layeris a refractory metal compound such as refractory metal nitrides (forexample TiN or HfN), refractory metal carbides (for example TiC or WC),or refractory metal borides (for example TiB or MoB). Barrier layerssuppress the diffusion of the silicon and metal atoms at thepolysilicon-metal interface, while offering a low resistivity and lowcontact resistance between the silicon and the barrier layer, andbetween the metal and the barrier layer. However, there is a problemwith such barrier layers in that, in an O₂ high temperature environment,they oxidize and disconnect the metal layer from the polysilicon plug.The oxide of the barrier layer may be formed either between the metaland the barrier layer, or between the polysilicon and the barrier layer.The latter situation is illustrated in FIG. 3, which shows metal oxidelayer 53 formed between barrier layer 52 and polysilicon plug 50. Ineither case, the oxide of the barrier layer affects the conductiveproperties of the metal contact by increasing the electric resistance inthe electrical connection region.

In an effort to reduce the oxidation problems posed by barrier layerssubjected to oxidizing environments, different techniques have beenintroduced into the IC fabrication. One of them is manipulating andcontrolling the deposition parameters of the barrier materials. Forexample, U.S. Pat. No. 4,976,839 discloses that the presence of an oxideat grain boundaries within a titanium nitride (TiN) barrier layerimproves the ability of the barrier layer to prevent the diffusion ofsilicon and aluminum. The reference further discloses a method forforming a barrier layer having large grain sizes by increasing thesubstrate temperature during sputtering, so that the formation of theoxide at the grain boundaries may be accomplished with a relativelylarge amount of oxygen, but without degradation in the filmconductivity.

Similarly, to further improve the characteristics of the barrier layers,certain metals, for which both the oxidized species (MeO) as well as theunoxidized species (Me) are electrically conducting, have been recentlyused as barrier layers between metal and polysilicon. Examples of thesemetals are ruthenium (Ru), platinum (Pt), or iridium (Ir), among others.Since these barrier layers are conductive in both the metal and theoxide forms, this approach is useful in that both the oxide and themetal forms slow down the oxidation front in an O₂ high temperatureenvironment. However, this technique has a drawback in that there willstill be some areas where the metal does not oxidize and, thus, thebarrier layer would consist of portions of pure metal species andportions of metal oxide.

Accordingly, there is a need for an improved method for slowing down theoxidation front in barrier layers used in contacts between metal andpolysilicon so that there is no oxidation at the polysilicon-metalinterface. There is also a need for metal-polysilicon contacts thatinhibit the diffusion of silicon and metal atoms at a contact interfaceand prevent the formation of oxides under high temperature O₂environment, as well as a method of forming such metal-polysiliconcontacts.

SUMMARY OF THE INVENTION

The present invention provides a method for forming a metal-polysiliconcontact that would be capable of tolerating an O₂ environment up toseveral hundred degrees Celsius for several hours. To prevent a metaloxide front, which is formed during a high temperature O₂ treatment fromreaching the metal film at the metal-polysilicon interface, the metalfilm is surrounded by a plurality of oxygen sinks. These oxygen sinksare oxidized before the metal film at the bottom of the plug isoxidized. Accordingly, the conductive connection between the polysiliconand any device built on top of the barrier layer is preserved.

Additional advantages of the present invention will be more apparentfrom the detailed description and accompanying drawings, whichillustrate preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a portion of aconventional memory DRAM device illustrating a metal-polysilicon contactformed in accordance with a method of the prior art.

FIG. 2 is a schematic cross-sectional view of the FIG. 1 deviceillustrating use of a barrier layer in a metal-polysilicon contactformed in accordance with the prior art.

FIG. 3 is a schematic cross-sectional view of the FIG. 2 devicedepicting the formation of an oxide layer between a polysilicon plug anda barrier layer.

FIG. 4 is a schematic cross-sectional view of a portion of a memory DRAMdevice, in which a metal-polysilicon contact according to a firstembodiment and method of the present invention will be formed.

FIG. 5 is a schematic cross sectional view of the FIG. 4 device at astage of processing subsequent to that shown in FIG. 4.

FIG. 6 is a schematic cross sectional view of the FIG. 5 device at astage of processing subsequent to that shown in FIG. 5.

FIG. 7 is a schematic cross sectional view of the FIG. 6 device at astage of processing subsequent to that shown in FIG. 6.

FIG. 8 is a schematic cross sectional view of the FIG. 7 device at astage of processing subsequent to that shown in FIG. 7.

FIG. 9 is a schematic cross sectional view of the FIG. 8 device at astage of processing subsequent to that shown in FIG. 8.

FIG. 10 is a schematic cross sectional view of the FIG. 9 device at astage of processing subsequent to that shown in FIG. 9.

FIG. 11 is a schematic cross sectional view of the FIG. 10 device at astage of processing subsequent to that shown in FIG. 10.

FIG. 12 is a schematic cross sectional view of the FIG. 11 device at astage of processing subsequent to that shown in FIG. 11.

FIG. 13 is a schematic cross sectional view of the FIG. 12 device at astage of processing subsequent to that shown in FIG. 12.

FIG. 14 is a schematic cross sectional view of the FIG. 13 device at astage of processing subsequent to that shown in FIG. 13.

FIG. 15 is a schematic cross sectional view of the FIG. 14 device at astage of processing subsequent to that shown in FIG. 14.

FIG. 16 is a schematic cross sectional view of the FIG. 15 device at astage of processing subsequent to that shown in FIG. 15, and depicting acapacitor formed over the metal-polysilicon contact.

FIG. 17 is a schematic cross sectional view of the FIG. 16 device at astage of processing subsequent to that shown in FIG. 16.

FIG. 18 is a schematic cross sectional view of the FIG. 14 device at astage of processing subsequent to that shown in FIG. 14, and inaccordance with a second embodiment of the present invention.

FIG. 19 is a schematic cross sectional view of the FIG. 14 device at astage of processing subsequent to that shown in FIG. 14, and inaccordance with a third embodiment of the present invention.

FIG. 20 is a schematic cross sectional view of the FIG. 18 device at astage of processing subsequent to that shown in FIG. 18, and depicting acapacitor formed over the metal-polysilicon contact.

FIG. 21 is an illustration of a computer system having a memory deviceemploying the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, reference is made to variousspecific embodiments in which the invention may be practiced. Theseembodiments are described with sufficient detail to enable those skilledin the art to practice the invention, and it is to be understood thatother embodiments may be employed, and that structural, logical, andelectrical changes may be made without departing from the spirit orscope of the present invention.

The term “substrate” used in the following description may include anysemiconductor-based structure that has an exposed silicon surface.Structure must be understood to include silicon-on insulator (SOI),silicon-on sapphire (SOS), doped and undoped semiconductors, epitaxiallayers of silicon supported by a base semiconductor foundation, andother semiconductor structures. The semiconductor need not besilicon-based. The semiconductor could be silicon-germanium, germanium,or gallium arsenide. When reference is made to substrate in thefollowing description, previous process steps may have been utilized toform regions or junctions in or on the base semiconductor or foundation.

The present invention provides a method for forming a metaloxide-metal-polysilicon contact capable of tolerating on oxygenenvironment up to several hundred degrees and for several hours. Theinvention provides one or more oxygen sink layers, which are oxidizedbefore the metal film is oxidized at the metal-polysilicon interface.The oxygen sink layers slow down the oxidation front of the metal film,so it does not reach the metal-polysilicon interface.

FIG. 4 depicts a conventional memory cell construction for a DRAM at anintermediate stage of the fabrication, in which a pair of memory cellshaving respective access transistors are formed on a substrate 12. TheFIG. 4 structure includes the substrate 12 having a well 13, which istypically doped to a predetermined conductivity, e.g. p-type or n-typedepending on whether NMOS or PMOS transistors will be formed therein.The structure further includes field oxide regions 14, conventionaldoped active areas 16 for use as source/drain regions, and a pair ofgate stacks 30, all formed according to well-known semiconductorprocessing techniques. The gate stacks 30 include an oxide layer 18, aconductive layer 20, such as polysilicon, nitride spacers 32 and anitride cap 22.

Above the gate oxide region 18, the polysilicon gates 20, and theprotective nitride regions 22,32, a first insulating layer 24 (FIG. 4)is disposed. Insulating layer 24 could be, for example,borophosphosilicate glass (BPSG), borosilicate glass (BSG), orphosphosilicate glass (PSG).

Reference is now made to FIG. 5, which for simplicity illustrates only alateral portion, for example a right side portion, of FIG. 4. This is aregion where a contact plug and an overlying capacitor structure will beformed. To create a contact opening 40 (FIG. 6) into semiconductorsubstrate 12 through the first insulating layer 24, a photoresistmaterial 26 (FIG. 5) is deposited and patterned using conventionalphotolithography steps. After patterning, an initial opening 27 (FIG. 5)is present in photoresist layer 26 for subsequent oxide etching. Thestructure of FIG. 5 is then etched, to form a contact opening 40 throughfirst insulating layer 24 and the photoresist layer is removed as shownin FIG. 6. The contact opening 40 is etched so that contact opening 40extends to a source/drain region 16 provided in well 13 of substrate 12.

Next, contact opening 40 is filled with a conductive material, such asdoped polysilicon, that is planarized down to or near the planar surfaceof the first insulating layer 24, to form a polysilicon plug or filler50, as illustrated in FIG. 7. The polysilicon plug 50 is thenanisotropically etched until its top surface is recessed below theplanar surface of the first insulating layer 24, so that a barrier layer52 (FIG. 8) can be deposited and planarized, as shown in FIG. 8. Thebarrier layer 52, preferably of titanium (Ti), is formed on thepolysilicon plug 50 by CVD, PVD, sputtering or evaporation, to athickness of about 60 to about 200 Angstroms. The titanium barrier layer52 will form titanium silicide (TiSi₂) during a later high temperatureanneal.

FIG. 9 illustrates the deposition of a second insulating layer 25, whichcould be, for example, a silicon oxide, borophosphosilicate glass(BPSG), borosilicate glass (BSG), phosphosilicate glass (PSG), ortetraethylortho silicate (TEOS). The second insulating layer 25 isdeposited over the barrier layer 52 and the first insulating layer 24.Again, using the same fabrication technique as the one used for theformation of contact opening 40 (FIG. 6) through the first insulatinglayer 24, a contact opening 41 (FIG. 10) is formed through the secondinsulating layer 25.

Subsequent to the formation of contact opening 41 of FIG. 10, a materialacting as an oxygen sink is deposited by using plasma, reactivesputtering or a conventional chemical vapor deposition to form a firstoxygen sink layer 60, as shown in FIG. 11, to a thickness of about 100Angstroms. Preferred materials for the first oxygen sink layer 60 arepolysilicon, aluminum nitride, titanium, titanium nitride, siliconnitride, or tantalum, among others. A characteristic of the sinkmaterial is that it oxidizes in a high temperature O₂ environment.Although some of the metals employed as oxygen sink oxidize and becometherefore nonconductive, this fact raises no problems because, in theembodiments described below, these metals are used strictly as oxygensinks and not as barrier layers. After deposition of the oxygen sinklayer 60, a spacer etch is employed to remove portions of the firstoxygen sink layer 60 inside the contact opening 41 and on the planarsurface of the second insulating layer 25, leaving only spacers 61formed of oxygen sink material on the side walls of contact opening 41,as illustrated in FIG. 12. The etch stops at the upper surface of thebarrier layer 52, without damaging, or etching into, the upper surfaceof the barrier layer 52.

Next, referring to FIG. 13, a layer 62 of conductive metal is formedinside the contact opening 41, over the upper surface of the barrierlayer 52, over the spacers 61 and over the upper surface of insulatinglayer 25. Although FIG. 13 illustrates the metal layer 62 as formed overthe upper surface of the second insulating layer 25, it is to beunderstood that metal layer 62 does not have to cover the secondinsulating layer 25. Depending on the type of devices that would befurther built to complete the formation of a DRAM memory cell, the metallayer 62 may or may not extend over the second insulating layer 25, aslong as it is formed inside of the contact opening 41.

Preferred materials for the conductive material layer 62 are metalconductors which, when oxidized, are still conductive, such as platinum(Pt), ruthenium (Ru), iridium (Ir), rhodium (Rh) and their respectiveoxides, or any other metal capable of forming a metal-barrierlayer-polysilicon contact on top of the polysilicon plug or filler 50.Metal layer 62 could be formed by any conventional method, such asdeposition or sputtering, to a thickness of approximately 100 to 300Angstroms.

A second oxygen sink layer 64 is next formed over the metal or metaloxide layer 62. This is illustrated in FIG. 14. The material for thissecond oxygen sink layer 64 may be, for example, a material whichoxidizes at high temperature O₂ environment, such as polysilicon,aluminum nitride, titanium nitride, silicon nitride, or tantalum. Thesecond oxygen sink layer 64 is then chemically metal polished (CMP) toform oxygen sink layer 64 of FIG. 15, on top of which another devicecould now be built.

For example, as shown in FIG. 16, a capacitor 80 formed of a firstruthenium oxide conductor (RuOx) layer 81, a tantalum oxide dielectric(TaOx) layer 82, and a second ruthenium oxide conductor (RuOx) layer 83can be formed in an opening created in a third insulating layer 27provided over the second insulating layer 25, at a position on top ofthe upper surface of the oxygen sink layer 64. The RuOx layer 81 isfabricated to be in contact with metal (or metal oxide) layer 62. Asknown in the art, during the fabrication process of the capacitor 80,the first ruthenium oxide conductor 81 requires an N₂/O₂ anneal, in anoxygen environment at high temperatures. Thus, during the anneal step,an oxygen front will move through the first ruthenium oxide conductor81, and move towards the oxygen sink layer 64, the metal layer 62 andthe barrier layer 52, towards the polysilicon plug 50, as shown in FIG.17. The oxygen front will be delayed by the oxygen sink layers 64 and61, but will nevertheless start oxidizing the metal layer 62 from thetop of the upper surface of the second insulating layer 25.

The oxygen sink layers 64 and 61 slow the movement of the oxygen frontso that it never reaches barrier layer 52 during the N₂/O₂ anneal. Thisis shown in FIG. 17. The upper portion of the metal layer 62 may oxidizeduring the anneal process to form a conductive metal oxide layer 62 a,but the remaining portion of the metal layer 62 is not oxidized duringthe anneal process as is shown by unoxidized metal layer 62 b. Thus, aneffective conductive path from capacitor conductor 81 to conductive plug50, through metal oxide layer 62 a, metal layer 62 b, and barrier layer52, is provided.

As a general proposition, it should be clear that the thicker the oxygensink layer 64, the slower the advancement of the oxygen front towardsthe barrier layer 52 and the polysilicon plug 50. Similarly, the greaterthe number of oxygen sink layers, the slower the advancement of theoxygen front towards the barrier layer 52. Of course, as well-known inthe art, the advancement of the oxygen front toward the polysilicon plug50 is also slowed down by employing a high aspect ratio contact, thatis, a contact with a small cross section A (FIG. 17 ) but a large heightL (FIG. 17) of the spacers 61 formed of oxygen sink material. A highaspect ratio is, for example, an aspect ratio of 25. Thus, ideally, theoxygen front is delayed by employing a multi-layer oxygen sink in a highaspect ratio metal-polysilicon contact.

FIG. 18 shows a second embodiment of the invention, which uses a firstand second oxygen sink spacers, 61 and 71, respectively, as well as afirst and second metal layers, 62 and 72, respectively, formed before afirst oxygen sink layer 64 is formed. Layers 62, 71, 72 and 64 aresequentially formed in a way similar to that employed for the formationof metal layer 62 (FIG. 13) and oxygen sink layer 64 (FIGS. 14-15),described with respect to the formation of the first embodiment of thepresent invention. As shown in FIG. 18, each of the layers 62, 71, 72and 64 is chemical mechanical polished (CMP) so that each of their uppersurfaces end at the upper surface of the second insulating layer 25,where a capacitor structure can be built in the manner shown anddescribed with reference to FIGS. 16 and 17. Of course, as explainedabove, layers 62, 71, 72 and 64 could extend over and cover the uppersurfaces of the second insulating layer 25, as long as the conductor 81of a fabricated overlying capacitor can connect with conductive layers62 and 72.

FIG. 19 illustrates yet a third embodiment of the present invention,which uses an oxygen sink layer that is not a good barrier to oxygendiffusion. An example of such oxygen sink material is titanium. In thisembodiment, nitride layers 93, 95 and 97 formed of silicon nitride, forexample, which is a good oxygen barrier, is used in connection withtitanium oxygen sink spacers 61 and 71, and titanium layer 64. Asexplained above, the first and second oxygen sink spacers, 61 and 71,formed of titanium, as well as a first and second metal layers, 62 and72, respectively, are formed before the titanium layer 64 is formed.Layers 93, 62, 95, 71, 72, 97 and 64 are sequentially formed in a waysimilar to that employed for the formation of metal layer 62 (FIG. 13)and oxygen sink layer 64 (FIGS. 14-15), described with respect to theformation of the first embodiment of the present invention. As shown inFIG. 19, when all of the layers 93, 62, 95, 71, 72, 97 and 64 areapplied, the structure is chemical mechanical polished (CMP) so thateach of their upper surfaces end at the upper surface of the secondinsulating layer 25, where a capacitor structure can be built.

FIG. 20 shows a capacitor 80 formed on the FIG. 18 structure. Thecapacitor 80 includes a first ruthenium oxide conductor layer 81, atantalum oxide dielectric layer 82, and a second ruthenium oxideconductor layer 83. The capacitor is formed so that conductor 81 is incontact with metal conductors 62 and 72. During the anneal step for thefabrication of the first ruthenium oxide conductor 81, the oxygen frontwill start from the first ruthenium oxide conductor 81 and move towardsthe polysilicon plug 50. The oxygen front is delayed by oxygen sinkspacers 61, 71, and 64 and will not reach the bottom of the metal layer62, which connects to the barrier layer 52, preventing therefore theformation of a barrier oxide layer, such as oxide layer 53 of FIG. 3.Further steps to create a functional memory cell containing the metaloxide-metal-polysilicon contact (FIGS. 15-20) may now be carried out toform other conductors or structures necessary for memory cellfabrication.

It should be noted again that the metal used for layers 62 and 72 mustbe one of those in which the metal oxide is conductive. Suitablematerials include platinum, rhodium, ruthenium, and iridium, amongothers.

A typical processor based system 400 which includes a memory circuit448, e.g. a DRAM, containing metal-polysilicon contacts according to thepresent invention is illustrated in FIG. 21. A processor system, such asa computer system, generally comprises a central processing unit (CPU)444, such as a microprocessor, a digital signal processor, or otherprogrammable digital logic device, which communicates with aninput/output (I/O) device 446 over a bus 452. The memory 448communicates with the central processing unit 444 over bus 452.

In the case of a computer system, the processor system may includeperipheral devices such as a floppy disk drive 454 and a compact disk(CD) ROM drive 456 which also communicate with CPU 444 over the bus 452.Memory 448 is preferably constructed as an integrated circuit, whichincludes metal-polysilicon contacts formed as previously described withrespect to the embodiments described in connection with FIGS. 4 to 20.The memory 448 may also be combined with the processor, e.g. CPU 444, ona single integrated circuit chip. It is also possible to employ theinvention in metal-polysilicon contacts within said processor.

Although the exemplary embodiments described above refer to one or twooxygen sink spacers and oxygen sink layers, and one or two metal layersfor the formation of the metal oxide-metal-polysilicon contact (FIGS.15-20), it is to be understood that the present invention contemplatesthe use of a plurality of oxygen sink spacers, oxygen sink layers, andmetal layers, and it is not limited by the illustrated embodiments.Accordingly, the above description and drawings are only to beconsidered illustrative of exemplary embodiments which achieve thefeatures and advantages of the present invention. Modification andsubstitutions to specific process conditions and structures can be madewithout departing from the spirit and scope of the present invention.Accordingly, the invention is not to be considered as being limited bythe foregoing description and drawings, but is only limited by the scopeof the appended claims.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A method for forming a metal-polysiliconcontact in a semiconductor device, comprising the acts of: forming aninsulating layer over a barrier layer residing over a polysilicon layer;forming a contact opening in said insulating layer; forming at least oneconductive layer and at least one oxygen sink layer in said contactopening, said oxygen sink layer being capable of absorbing oxygen; andforming a semiconductor device over said at least one oxygen sink layerand said conductive layer.
 2. The method of claim 1, wherein saidsemiconductor device is a capacitor formed in contact with saidconductive layer.
 3. The method of claim 2 further comprising the act ofheat annealing said capacitor.
 4. The method of claim 3, wherein saidact of heat annealing said capacitor is conducted in an nitrogen/oxygenenvironment.
 5. The method of claim 2, wherein said capacitor comprisesa first capacitor electrode formed over said conductive layer, adielectric layer formed over said first capacitor electrode, and asecond capacitor electrode formed over said dielectric layer.
 6. Themethod of claim 2, wherein said capacitor comprises a first rutheniumoxide electrode, a tantalum oxide dielectric layer, and a secondruthenium oxide electrode.
 7. The method of claim 1, wherein said atleast one oxygen sink layer is formed of a material selected from thegroup consisting of polysilicon, aluminum nitride, titanium nitride,tantalum, and silicon nitride.
 8. The method of claim 3, wherein said atleast one oxygen sink layer is formed of titanium.
 9. A method forforming a metal-polysilicon contact in a semiconductor device,comprising the acts of: forming an insulating layer over a barrier layerresiding over a polysilicon layer; forming a contact opening in saidinsulating layer; forming at least one conductive layer and at least oneoxygen sink layer in said contact opening, said oxygen sink layer beingcapable of absorbing oxygen and being formed as a plurality of spacedoxygen sink layers; and forming a semiconductor device over said atleast one oxygen sink layer and said conductive layer.
 10. The method ofclaim 9, wherein said plurality of spaced oxygen sink layers comprisestwo oxygen sink layers separated by one conductive layer.
 11. The methodof claim 9, wherein said plurality of spaced oxygen sink layerscomprises three oxygen sink layers separated by two contactingconductive layers.
 12. A method for fabricating a metal-polysiliconcontact in a semiconductor device, comprising the acts of: forming aninsulating layer over a barrier layer residing over a polysilicon layer;forming a contact opening in said insulating layer; forming at least oneconductive layer and at least one oxygen sink layer in said contactopening, said oxygen sink layer being capable of absorbing oxygen;forming a capacitive element over and in contact with said conductivelayer; and subjecting said capacitive element to a nitrogen/oxygenanneal treatment.
 13. The method of claim 12, wherein said capacitiveelement comprises a first ruthenium oxide electrode, a tantalum oxidedielectric layer, and a second ruthenium oxide electrode.
 14. The methodof claim 12, wherein said oxygen sink layer is formed of a materialselected from the group consisting of polysilicon, aluminum nitride,titanium nitride, tantalum, and silicon nitride.
 15. A method forfabricating a metal-polysilicon contact in a semiconductor device,comprising the acts of: forming an insulating layer over a barrier layerresiding over a polysilicon layer; forming a contact opening in saidinsulating layer; forming at least one conductive layer and at least oneoxygen sink layer in said contact opening, said oxygen sink layer beingcapable of absorbing oxygen and being formed as a plurality of spacedoxygen sink layers; forming a capacitive element over and in contactwith said conductive layer; and subjecting said capacitive element to anitrogen/oxygen anneal treatment.
 16. The method of claim 15, whereinsaid plurality of spaced oxygen sink layers comprises two oxygen sinklayers separated by one conductive layer.
 17. The method of claim 25,wherein said plurality of spaced oxygen sink layers comprises threeoxygen sink layers separated by two contacting conductive layers.
 18. Amethod for fabricating a metal-polysilicon contact in a semiconductordevice, comprising the steps of: forming an insulating layer over abarrier layer residing over a polysilicon layer; forming a contactopening in said insulating layer; and forming a first oxygen sink spacerin said contact opening, said first oxygen sink spacer being capable ofabsorbing oxygen; forming a first conductive layer in said contactopening and in contact with said first oxygen sink spacer; forming asecond oxygen sink spacer in said contact opening and in contact withsaid first conductive layer, said second oxygen sink spacer beingcapable of absorbing oxygen; forming a second conductive layer in saidcontact opening and in contact with said second oxygen sink spacer, saidsecond conductive layer being in contact with said first conductivelayer; forming an oxygen sink layer in said contact opening and incontact with said second conductive layer; and forming a capacitor oversaid oxygen sink layer and said second conductive layer.
 19. The methodof claim 18, wherein said oxygen sink layer is formed of a materialselected from the group consisting of polysilicon, aluminum nitride,titanium nitride, tantalum, and silicon nitride.
 20. The method of claim18, wherein each of said first and second oxygen sink spacers is formedof a material selected from the group consisting of polysilicon,aluminum nitride, titanium nitride, titanium, tantalum, and siliconnitride.
 21. The method of claim 18, wherein said capacitor comprises afirst ruthenium oxide electrode, a tantalum oxide dielectric layer, anda second ruthenium oxide electrode.
 22. A method of forming ametal-polysilicon contact in a semiconductor device, comprising thesteps of: forming an insulating layer over a barrier layer residing overa polysilicon layer; forming a contact opening in said insulating layer;and forming a first oxygen barrier layer in said contact opening;forming a first oxygen sink spacer in said contact opening and incontact with said first oxygen barrier layer, said first oxygen sinkspacer being capable of absorbing oxygen; forming a first conductivelayer in said contact opening and in contact with said first oxygen sinkspacer; forming a second oxygen barrier layer in said contact openingand in contact with said first conductive layer; forming a second oxygensink spacer in said contact opening and in contact with said secondoxygen barrier layer, said second oxygen sink spacer being capable ofabsorbing oxygen; forming a second conductive layer in said contactopening and in contact with said second oxygen sink spacer, said secondconductive layer being in contact with said first conductive layer;forming a third oxygen barrier layer in said contact opening and incontact with said second conductive layer; forming an oxygen sink layerin said contact opening and in contact with said third oxygen barrierlayer; and forming a capacitor over said oxygen sink layer and saidsecond conductive layer.
 23. The method of claim 22, wherein said oxygensink layer is formed of a material selected from the group consisting ofpolysilicon, aluminum titanium nitride, tantalum, and silicon nitride.24. The method of claim 22, wherein each of said first and second oxygensink spacers is formed of a material selected from the group consistingof polysilicon, aluminum nitride, titanium nitride, titanium, tantalum,and silicon nitride.
 25. The method of claim 22, wherein each of saidfirst, second and third oxygen barrier layers is formed of siliconnitride.
 26. The method of claim 22, wherein said capacitor comprises afirst ruthenium oxide electrode, a tantalum oxide dielectric layer, anda second ruthenium oxide electrode.